FUNCTION 3 IN 1: Contains tachometer, hour meter, service timers ;Help you track how many hours your engine running.When engine is off, display shows total run time of engine and remains visible. Total hours can be reset ; 0.1 hours accuracy. POWERED BY LITHIUM BATTERY: The tachometer is powered by one CR2450 lithium battery(can't replace ). No external power connections are required. Wide application: Boat, generator, lawn mower, chainsaw, outboard, motorcycle, motocross, ATV, snowmobile, UTV, gasoline engine. HOW TO OBSERVE: When the engine is on, the display will read the RPM of the engine. When the engine is off, the display will switch to total run time and remains visible. RPM Display from 0 to 20,000 RPM with 10 RPM accuracy. EASY TO INSTALL: Tiny tach wired Tachometer and Engine RPM gauge is super easy installation, gets the job done with minimal complication, hall effect gas generator rpm tester tool hr metre just need wrap the single black wire to contact the spark plug fire of your engine(turn at least 5 rounds to make sure the connection is tight). SUITABLE FOR: Waterproof universal hour meter suitable for all two stroke & four stroke gasoline engines. resettable electronic tachometer can reset total works hour and maintenance time, monitor the engine status in order to repair in time.